Heavy machinery, such as off-highway trucks, are commonly used in mining, heavy construction, quarrying, and other applications. Although such machines are traditionally directly driven via an internal combustion engine, the extensive fuel consumption and mechanical complexity of such systems has spurred wide-ranging exploration of alternative power systems.
One advance that has improved efficiency associated with the use of heavy machinery is the adoption of Alternating Current (AC) or electric drive systems. Electric drive systems for machines typically include a power circuit that selectively activates one or more drive motors at a desired torque. Each of the drive motors is connected to a wheel or other traction device that operates to propel the machine. An electric drive system includes a prime mover, for example, an internal combustion engine, that drives a generator. The generator produces electrical power that is often conditioned, and ultimately used to drive the motor. The motor transforms the electrical power back into mechanical power that drives the wheel and propels the vehicle. Electric drive systems typically require less maintenance and thus, have lower life cycle costs.
However, there are other faults associated with such machines that warrant attention in order to provide optimal machine operation. For instance, the drive systems on transmission driven vehicles are inherently stable insofar as the load applied to the engine is generated directly from ground force exertion (causing acceleration). Hence, as the vehicle accelerates, the load can steadily increase. Electric drive systems, however, may include an intermediate state of loading, the electrical system, which adds a degree of freedom. This added degree of freedom disconnects the mechanical connection between the ground and the engine, thus making the system less stable. For example, the load on the generator, and thus the primary power source, can be increased in a step-wise manner instead of the more gradual manner usually experienced with engine driven machines. Such sudden increases in demanded power are not easily accommodated, and in some cases may cause the primary power source or the generator to lag or ignore the power command, or in fact, to fail. This and other shortcomings in the state of the art are addressed by aspects of the disclosed principles.